Computerised simulation programs have been used to investigate a number of archaeological and historical problems, including population dispersals (Levison, Ward & Webb 1973; Thome & Raymond 1989), exploration strategies (Irwin et al. 1990), population origins (Callaghan 1999; 2003a), maritime trade and interaction (Callaghan 2001) and trans-Pacific contacts between Japan and North America (Callaghan 2003b). A computer simulation designed to answer various problems relating to prehistoric and historic voyaging is used here to investigate the difficulty of maintaining contact between Ecuador and West Mexico and to determine the level of skill necessary to make these trips safely.

The simulation program

The simulation program used here is a much more advanced version of the one used in Callaghan 1999 and 2001. This second-generation program is based on the United States Navy Marine Climatic Atlas (US Navy 1995) and has been expanded to include all of the world's seas and oceans with the exception of Arctic waters. The data is organised in a finer resolution of one degree Marsden squares (one degree of longitude by one degree of latitude) rather than two degree Marsden squares. In particular, this allows the effects of smaller and more variable currents to be accurately reflected in the outcomes. The advanced program also automatically shifts to the database for the following month after the month originally selected for has expired. This feature better reflects the reality of changing wind and current conditions over long voyages. A conversion to spherical co-ordinates has also been added in order to increase positional accuracy outside of the tropics. Finally, the program allows the operator to change the heading of a vessel during a voyage to reflect decisions made by the crew. This last feature is important when assessing the level of skill required to reach a selected target.

In its basic operation, the program makes a random selection of direction and speed for wind and current from the Marine Climatic Atlas (US Navy 1995) database. These data are compiled from ship reports and other sources since the early nineteenth century. A course is chosen for the vessel, unless undirected drift voyages are being investigated. Performance data, calculated using either naval architecture programs or field tests, are then used to calculate the ratio of vessel velocity to true wind velocity. Wind and current forces are allowed to affect the vessel for a twenty-four hour period, and a new position for the vessel is then calculated. A new heading is chosen every twenty-four hours to move the vessel in the desired direction.

Watercraft

The results of extensive research conducted by Clinton Edwards (1965a, 1965b, 1969, 1978) indicate that sailing rafts, sailed canoes, and paddled canoes were likely to have been used by Ecuadorian merchants during the period under consideration. Sailing canoes, which would have been more effective than paddling over long distances, appear not to have been adopted in northern Ecuador until the time of Spanish contact in the early part of the sixteenth century (Edwards 1965a: 356). Unfortunately, as Edwards points out, there is little archaeological evidence that suggests a preference for any of these watercraft in any possible prehistoric trade with West Mexico. …

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